Machine Descriptions
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A machine description has two parts: a file of instruction patterns
(`.md' file) and a C header file of macro definitions.
The `.md' file for a target machine contains a pattern for each
instruction that the target machine supports (or at least each
instruction that is worth telling the compiler about). It may also
contain comments. A semicolon causes the rest of the line to be a
comment, unless the semicolon is inside a quoted string.
See the next chapter for information on the C header file.